Circuit



Oct. 27,1970 A. v1'. 'NIELSEN ETAL 3,537,058

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Oct. 27, 1970 A.1.N|El.sEN ETAL 3,537,098

4 CIRCUIT Filed sept. 2v. 196e s sheets-sheet 2 INVENT ORS ASGE?/WE'LSEN R/CHARD R. WHEELOCI( ATTO EYS Oct. 27,1970 A. T. NIELSYEN ETAI-3,537,098

v 3H CIRCIT Filed sepnxzv, 196e s sheets-sheet a F76. 30 FIG. 3E

' /6`. 3 INvEm-ons ASGER rA//ELsE/v R/cHARa e WEE/.00K

U.S. Cl. 340-324 8 Claims ABSTRACT 0F THE DISCLOSURE Symbol generatorsincluding a cathode ray tube, a system for applying successive pairs ofsignals to the deflection coils of the tube to cause the electron beamto trace a character on the face of the tube as a series ofinterconnected strokes, and a beam intensity control for maintaining theintensity of successive strokes generally uniform.

This invention pertains basically to a system of character generationfor graphically reproducing and visually displaying selected charactersin response to electric signals representing such characters lbut in itsbroader aspects is applicable more generally to curve plotting and linegeneration from data indicative of the coordinates of successive pointson the curve to be plotted.

More specifically the invention pertains to a system for displayingalphabetic, numeric and other predetermined characters on a cathode raytube in accordance with signals indicative of the character to bedisplayed received thereby.

A number of prior art devices exist by the use of which it is possibleto generate alphanumeric characters on the phosphor screen of a cathoderay tube. Three principal types of cathode ray tube character displayunits are known. A Iirst type includes units in which a shaped electronbeam is generated by the electronic illumination of a mask inside thetube. The mask is provided with a plurality of apertures each having theshape of a different letter or number, and by directing an electron beamonto the mask from the electron gun a shaped beam is provided. By theuse of a deflection system the shaped beam is positioned on the screenas required. A second type is that in which a scanning raster is formedat a desired position on the screen; and the tube is `unblanked to forma character composed of line segments in a manner similar to thecomposition of a television picture. Still a third type of unit is thatin which an electron beam is rst positioned to a reference point andthen is caused to trace out the character through the application of theX and Y component `functions to the deflection system.

This invention relates to cathode ray tube character display systems ofthis last type.

In accordance with the present invention input data to be displayed istransmitted in coded form, and is decoded by suitable means to selectthe corresponding characters in a character programming device. Theprogramming device comprises a plurality of units (corresponding innumber to the number of characters to be selectively displayed), each ofwhich is adapted, in conjunction with a sequential timing device, togenerate unique sequence signals of varying amplitudes for a givencharacter to control the generation of a visual display of suchcharacter upon a cathode ray tube or other display device.

A display generating unit generates selected horizontal nited Statesaten and vertical sweep voltage wave forms, and beam intensity controlsignals, which are applied to the vertical and horizontal deflectionsystems and intensity control systems of the display tube cause theelectron beam to trace the selected character on the face thereof.

In prior patents such as exemplified by Palrniter, No. 3,047,851, datedJuly 3l, 1962 and entitled Electronic Character Generating andDisplaying Apparatus, it is old to displace a cathode ray beam through apredetermined number of locations on the face of the tube, in accordancewith the character being generated, so that phosphor retentvity willproduce a continuous display. Customarily, the locations through whichthe beam is directed are determined by a matrix uniqe to the characterto 'be generated, and is effected under control of a timing circuitwhich triggers the matrix for sequential control of the beam, from apredetermined starting point, over the face of the tube. The beamcontrol pulses are emitted in units of fixed amplitude and timeduration, as X and Y coordinate increments, and are integrated to form acontinuous signal to the horizontal and vertical deflection controlelements of the cathode ray tube.

In other patents of the prior art, such as Dell, No. 3,090,041, issuedMay 14, 1943 for Character Generation and Display, the beam controlpulses are of variable amplitude and are applied to the deflectionplates without integration to trace a distinctly dotted pattern, inwhich the dots in the character outlines are Imore or less pronounceddepending on the closeness of their location.

As distinct from the above prior art, the present invention utilizesindividual character matrixes which control the generation of pulsetrains of variable amplitudes which are determinative of sequential beamlocations in terms of X and Y coordinates, and these are processed foreach successive beam location to determine the algebraic differencebetween each successive pair of X and Y values respectively, and thedifferences obtained are integrated to control beam displacement.

The system has definite advantages over the prior art in that theresultant characters displayed are generatedv in continuous lines thesegments of which while varying in length are maintained atsubstantially constant inten; sity. In addition, the present inventionprovides high speed and better character definition independently ofcharacter size and location. To provide a display device control systemwhich will achieve these results is the basic object of this invention.

These and other objects of the present invention will become Imore fullyapparent by reference to the appended claims and as the followingdetailed description proceeds in reference to the accompanying drawingswherein:

FIG. l is a diagram illustrating the present invention;

FIG. 2 is a diagram illustrating the details of the intensity control ofthe circuit of FIG. l; and

FIG. 3 is a series of coordinate diagrams illustrating the display of atypical character and the several signals generated in the circuit ofFIG. l for the display of that character upon a cathode ray tube.

Referring now to FIG. l, the circuit of the present invention respondsto a coded data indicative input identified by the simultaneousselective application of input signals to certain of the six input linesL, to Ls in a pattern indicative of the character to be displayed. Thepattern of input signals in lines L1 to L6 is sensed and decoded by thedecoding and selection network 10 to energize a single one of itssixty-four output lines S1 to S64 in accord with 3 the pattern of theinput signals appearing in lines L1-L6.

The thus selected output lines S1 to S64 activates the one of thecharacter generator matrixes C-l to C-74 to which it is connected.

Each of the matrixes C-1 to C-64 has sixteen X coordinate output linesX1 to X16, sixteen Y coordinate output lines Y1 to Y16, and sixteen Zcoordinate output lines Z1 t0 216.

The lines X1 to X16 are each connected to one of the input terminals ofsixteen distinct two-input AND gates 16. The other inputs to these ANDgates are connected respectively to the input terminals T1 to T16 fromthe timing circuits 14. Input terminals T1 to T16 are successivelyactivated in sixteen successive time intervals so that a time sequentialsignal appears at the common output of the X AND gates the magnitude ofwhich, in each of its sixteen successive time intervals, is proportionalto the magnitude of the signal appearing at the input terminalsconnected to X1 and X16 respectively. Such a signal is shown at X infull lines in FIG. 3E. The magnitude of the signal at the inputterminals connected to X1 to X16 depends on the character to bedisplayed. For example, for the numeral 2, shown in FIG. 3C, theseinputs will be:

Terminal connected to Voltage (units) These same voltages aresimultaneously applied from leads X1 to X16 to the inputs of the X ANDgates 18 each lead being individually connected to one of the two inputterminals of one of the sixteen X AND gates 18. The other terminals ofthe X' AND gates 18 are successively activated from the timing circuit14 through the input terminals T1' to T16. There is a one time intervaltime delay between the activation of the input terminals T1 to T16 andthe input terminals T1' to T16. That is, for example, T2 and T1' areactivated simultaneously as are T6 and T2', T4 and T6', etc.

As a result a signal X appears at the common output of the X AND gates18 which is identical with that appearing at the output of the X ANDgates but delayed by one time interval. This is indicated for thenumeral 2 at X in FIG. 3E in dash lines.

The signal X is fed through an X inverter 20 to produce a signal -X. Theoutput of the X AND gates 16 and of the X inverter 20 are connected tothe inputs of the X integrator 22, the resultant input signal being X-Xwhich for the numeral 2 is shown in FIG. 3D. The output of the Xintegrator 22 is a continuous signal AX substantially of the formindicated in dot-dash lines in FIG. 3E at AX.

Since the rate of change of the output of the X integrator 22 isproportional to the amplitude of the input signal, (X-X), one can byproper selection of the integrator time constant cause the outputVoltage to describe a curve A X that connects the corner of thestaircase voltage X as indicated in FIG. 3E.

The sixteen Y AND gates 24 and sixteen Y AND gates 26 are similarlyconnected to sixteen input terminals Y1 to Y16 from the charactermatrixes C-1 to C-64 and to the input terminals T1 to T16 and T1' toT16' from the timing 4 circuit 14 to produce signals Y and Y as shownfor the numeral 2 in FIG. 3B. When the Y signal is inverted in the Yinverter 28 to produce a -Y signal and combined with the Y signal, theresultant input (Y-Y) to the Y integrator 30 is as shown in FIG. 3A andthe output is as indicated in dot-dash lines in FIG. 3B as AY for thenumeral 2. The input voltages at Y1 to Y16 for the numeral 2 are:

Terminal: Voltage (units) Y1 1 Y-7 1l Y-S 16 Y-9 19 Y-l() 24 Y-11 29Y-12 32 Y-13 33 Y-14 32 Y-15 .28

When AX and AY signals that are generated in this manner are impressedin the horizontal and vertical deflection system of a cathode ray tube31, the outline of an alphanumeric character or other programmed symbolcan be drawn as indicated by the display of the number 2 in FIG. 3C.

As is apparent in FIG. 3, the several sub-figures have been plotted onthe common coordinates so that the X and Y voltages and beam positionscan be readily compared for the successive time intervals as can the X,X', (X-X), Y, Y and (Y-Y) values.

From an analysis of FIGS. 3B, 3C and 3E, it is apparent that certainstrokes must be blank and others must be visible. For the numeral 2 asdisplayed in FIG. 3C, these are strokes 1, 2 and 16. For control of theblanking and unblanking the character matrixes C-l to C-64 are eachconnected to one of the inputs Z1 to Z16 of the sixteen Z AND gates 32.The other inputs of these Z AND gates 32 being connected respectively tothe timing circuit input lines T1 to T16 respectively. The inputs Z1 toZ16 from the selected character matrixes C-1 to C-64 are such that, whena blank stroke is required within a character, there is a positiveoutput on the line Z from the Z AND gates 32 synchronized with the X,X', Y and Y' signals. The Z signal through a ip-op (not shown) istransmitted to the intensity control 34 and the Z amplier 36 to thecontrol grid of the cathode ray tube 31.

The intensity control 34 contains two independent circuits for blankingand unblanking, and a ip-flop is set and reset by the leading andtrailing edges of the time pulses if a Z-diode is programmed in thecharacter matrix for a given line segment.

This applies in almost all cases where the electronic beam is to bemoved from the character reference point (lower left corner of characterrectangle FIG. 3C), to the beginning of the character. Either one or twostrokes are used depending on the distance and both must be blanked. Oneor two Z-diodes in time 1 and/or 2 causes the Hip-op in the intensitycontrol 34 to set at the beginning of time pulse 1 and reset at the endof time pulse 1 or 2. This way the electronic beam is blanked as itmoves from reference position to beginning of character.

As is apparent from FIG. 3C, the time intervals are constant but thedistance through which the beam is deflected in different time intervalsvaries. Unless compensated for, there would be variations in lightintensity of the diierent segments of the character traced due tovariations in beam velocity. In the present invention the beam intensityis controlled as will now be explained.

The magnitude of the signal X-X is directly proportional to thehorizontal component of the stroke and is therefore also proportional tothe horizontal velocity component. If dx/dt and dy/dt Were addeddirectly, an error of 2-l.4/ 1.4 would result. This is approximately43%. By selecting the larger component and adding this to one-half ofthe smaller component, the error can be reduced to 16%. A small analogcomputer is used to accomplish this. This computer is the circuitdenominated intensity control in FIG. 1 and shown in detail in FIG. 2.

The circuit on FIG. 2 generates a signal that is proportional to S L-rwhere L is the length of the longest component AX or AY for a givenstroke and S is the length of the shortest component. This Way controlsthe intensity with an error of only i6%.

Since the lines carrying the X and the inverted X' signals and Y and theinverted Y signals in the other case are the inputs to the intensitycontrol 34, the resultant input is X-X and Y-Y'.

The operation of the circuit in FIG. 2 is as follows.

The two differential amplifiers 38 and 40 generate two outputs each. Inamplifier 38 they are (X-X) and -(X-X'); for amplifier 40 they are (Y-Y)and (Y-Y').

Therefore independent of the sign of X and X and Y and Y at the input,one of the two outputs of each of the amplifiers 38 and 4f) will benegative, and one will be positive.

Diodes 42 and 44 form an OR gate. Only the diode that has its anodeconnected to the positive output will conduct, thus back biasing theother diode. The same is true for diodes 46 and 48.

Diodes 50 and 52 complete the OR functions in such a Way that the mostpositive of all four amplifier outputs will cause a current to owthrough resistor 54 to the summing junction of amplifier 36.

This current is proportioned to L. Diodes 58, 60; 62 and 64 form tWoother OR gates selecting the negative outputs of each amplifier 38 and40.

Diodes 66 and 68 and the resistor 70, to -V selects the least negativeof the two negative outputs and thus function -S is generated. Itsupplies current through resistor 72 (the value of which is twice thatof the resistor 54) to the summing junction. The output of amplifier 36is thus This signal is applied to the control grid of the cathode raytube during the strokes of the character during which the tube is notblanked by the Z signal to maintain the intensity of the strokes uniformWithin i6% regardless of the variations in their lengths.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentinvention is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A symbol generator comprising:

(a) a cathode ray tube having a pair of beam defiection control inputs,display means on which a character can be generated by so defiecting anelectron beam impinging on said display means by the application ofvarying voltage signals to the beam deflection control inputs as tocause said beam to trace out the character, and a beam intensity controlinput responsive to the application of a signal thereto to vary theintensity of the electron beam;

(b) means for generating and applying pairs of beam defiecting signalsto said control inputs in each of successive periods of equal duration,whereby the character is traced as a series of strokes which are ofequal duration but of varying length, position and direction, saidsignal generating means comprising, for each beam deflection controlinput, means for producing a first pulse train, means for producing asecond pulse train identical to the first pulse train but with eachpulse thereof following the identical pulse of the first train by aperiod equal to the duration of one stroke, means for inverting thepulses in the second pulse train, means for summing the inverted pulsesand the pulses of the first pulse train and for integrating the summedpulses to produce an unbroken beam deflecting signal for application tothe associated beam deflection control input; and

(c) means for generating and applying to the intensity control inputsimultaneously with the application of said pairs of signals to the beamdeflection control inputs signals which will cause said beam intensitycontrol to so vary the beam intensity as to maintain the intensity ofsuccessive strokes generally uniform.

2. The symbol generator of claim 1, wherein each means for generatingfirst and second pulse trains comprises first and second AND gates eachhaving a plurality of coded pulse inputs equal to the number of pulsetrain pulses and a like number of timing pulse inputs, said gates beingcapable of transmitting pulses when corresponding code pulse inputs andtiming pulse inputs are energized, means for supplying coded pulsesequal to the number of pulses in the train simultaneously to the codedpulse inputs of the first and second AND gates, and timing means forsuccessively energizing the timing pulse inputs of the first and secondAND gates with a delay between energization of corresponding timingpulse inputs of the first and second AND gates equal to the duration ofone stroke, whereby said pulses are transmitted through the first andsecond AND gates in the same predetermined sequence with the pulsesbeing transmitted first through the first AND gate and then through thesecond AND gate.

3. The symbol generator of claim 2', wherein the inverter of each signalgenerating means is operatively connected to the output of the secondAND gate thereof and the integrating means of each signal generatingmeans has one input connected to the output of the first AND gatethereof, a second input connected to the output of the inverter thereof,and an output connected to the associated beam deflection control input.

4. The symbol generator of claim 2, wherein the means for applyingsignals to said beam intensity control input comprises blanking meansoperatively connected to said beam intensity control for causing thelatter to prevent the generation of a trace on said display means duringthose of the equal duration periods when a positive pulse is applied tosaid control, said last-mentioned means including a third AND gatecapable of transmitting only positive pulses, said third AND gate havingcoded pulse inputs connected to the coded pulse supplying means andtiming pulse inputs connected to said timing means, and means connectingsaid third AND gate to said beam intensity control.

5. A symbol generator comprising:

(a) a cathode ray tube having a pair of beam deflection control inputs,display means on which a character can be generated by so deflecting anelectron beam impinging on said display means by the application ofvarying voltage signals to said beam deflection control inputs as tocause said beam to trace out the character, and a beam intensity controlinput responsive to the application of a signal thereto to vary theintensity of the electron beam;

(b) means for generating and applying to said control inputs in each ofsuccessive periods of equal duration pairs of signals which so deflectthe electron beam that the character is traced as a series of strokeswhich are of equal duration but of varying length, position, anddirection and which are comprised of components determined by thesignals applied to the control inputs; and

(c) means for generating and applying to the intensity control inputsimultaneously with the application of said pairs of signals to the beamdeflection control inputs signals which will cause said beam intensitycontrol to so vary the beam intensity as to maintain the intensity ofthe successive strokes generally the same, said last-mentioned meanscomprising means for generating in each period in which a stroke istraced a signal which is proportional to the difference between thelength of the longer component of the stroke and one-half the length ofthe shorter component of the stroke and means for applying the signalsthus generated to the intensity control input in said successiveperiods.

6. The symbol generator of claim 5, together with blanking meansoperatively connected to said signal generating means and said beamintensity control for causing the latter to prevent the generation of atrace on said display means during at least one of said equal durationperiods.

7. A symbol generator comprising a cathode ray tube having a pair ofbeam deflection control inputs, display means on which a character canbe generated by so deliecting an electron beam impinging on said displaymeans by the application of varying voltage signals to the beamdeflection control inputs as to cause said beam to trace out thecharacter, and a beam intensity control input responsive to theapplication of a signal thereto to vary the intensity of the electronbeam, means for generating and applying pairs of beam deflecting signalsto said control inputs in each of successive periods of equal durationwhereby the character is traced as a series of strokes which are ofequal duration but of varying length, position and direction and whichare comprised of components determined by the signals applied to thecontrol inputs, said signal generating means comprising, for each beamdeflection control input, means for producing a first pulse train, meansfor producing a second pulse train identical to the first pulse trainbut with each pulse thereof following the identical pulse of the lirsttrain by a period equal to the duration of one stroke, means forinverting the pulses in said second pulse train, and means for summingthe inverted pulses and the pulses of the first pulse train and forintegrating the summed pulses to produce an unbroken beam deliectingsignal for application to the associated beam deflection control input,and means for generating and applying to the intensity control inputsimultaneously with the application of the pair of signals to the beamdeflection control inputs in each period in which a stroke is generateda signal which will cause the beam intensity control to so vary the beamintensity as to maintain the intensity of successive strokes generallyuniform, said last-mentioned means comprising a first differentialamplifier for generating two signals of equal magnitude and oppositepolarity which are proportional to the magnitude of one of thecomponents of the stroke and a second differential amplilier forgenerating two signals of equal magnitude and opposite polarity whichare proportional to the magnitude of the other of the components of thestroke, a third amplifier, means for passing to the summing junction ofthe third amplifier the most positive of the four signals generated bythe differential amplifiers, means for reducing the magnitude byone-half and transmitting to the summing junction, of the thirdamplifier the least negative of said four signals, and means connectingthe output of said third amplifier to the intensity control input of thecathode ray tube.

8. The symbol generator of claim 7, wherein:

(a) the means for selecting the most positive of the four signalsgenerated by the differential amplifiers comprises an OR gate connectedto each of the differential amplifiers, said OR gates being connected tooutputs of the differential amplifiers which are capable of transmittingonly signals of positive polarity, and a diode connected between each ofsaid OR gates and the summing junction of the third amplifier, saiddiodes being connected in parallel and in opposed relationship, wherebyonly the diode to which the more positive signal is applied willconduct;

(b) the means for selecting the least negative of said four signalscomprises a further OR gate connected to each of said differentialamplifiers, the further OR gates being connected to the outputs of saiddifferential amplifiers which are capable of transmitting only signalsof negative polarity, and a further diode connected between each of thefurther OR gates and the summing junction of the third ampliers, thefurther diodes being connected in parallel and in opposed relationship,whereby only the further diode to which the least negative signal isapplied will conduct; and

(c) the means for reducing by one-half the magnitude of the leastnegative of said signals comprises a resistance connected in series withand between the further diodes and said summing junction.

References Cited UNITED STATES PATENTS 3,047,851 7/l962 Palmiter340-3241 3,205,488 9/1965 Lumpkin 340-3241 3,234,534 2/1966 Todman340-324-l 3,333,147 7/1967 Henderson 340324.1 3,382,487 5/1968 Sharon etal. 340-324.1

ALVIN H. WARING, Primary Examiner M. M. CURTIS, Assistant Examiner U.S.Cl. X.R.

